1. Field of the Invention
The present invention relates to an exterior environment recognition device and an exterior environment recognition method for recognizing environment outside of a subject vehicle.
2. Description of Related Art
Conventionally, there is known a technique that identifies a target object such as an obstacle and a vehicle located in front of a subject vehicle and avoids a collision against the identified target object (collision avoiding control) and a technique that performs control so as to maintain a safe distance between the subject vehicle and a preceding vehicle (cruise control) (for example, Japanese Patent No. 3349060). In many of these techniques, a preceding vehicle is tracked to update the position information thereof, and calculate the travelling speed and the like of the preceding vehicle. The result of this calculation is used for brake (braking) control and cruise control, for example.
However, it is difficult to smoothly carry out cruise control by simply calculating the behavior of the preceding vehicle. More smooth cruise control can be achieved by, for example, incorporating a human-like processing of viewing and recognizing whether a brake lamp of the preceding vehicle is turned on or not and the like, and predicting deceleration operation of the preceding vehicle.
As such a technique for detecting whether the brake lamp of the preceding vehicle is turned on or not, there is a technique for distinguishing between the brake lamp and the tail lamp on the basis of acceleration/deceleration of the preceding vehicle (for example, Japanese Unexamined Patent Application Publication (JP-A) No. 2005-1425). A technique for detecting a brake lamp in an ON state on the basis of change of luminance or change of the size of a detection area of a tail lamp and determining a deceleration state of a preceding vehicle (for example, Japanese Patent No. 3872179) is also disclosed, and a technique using a histogram distribution of lightness in a red color area to determine whether a brake lamp is turned on by means of standard deviation and the like (for example, JP-A No. 9-267686) is also disclosed.
In the technique of JP-A No. 2005-1425 described above, the brake lamp is distinguished on the basis of the acceleration/deceleration of the preceding vehicle, but the cause of the deceleration may not be necessarily the brake operation. Moreover, it takes some time from when a driver performs brake operation to when the vehicle actually decelerates, and therefore, the brake operation is determined with a delay since the brake lamp is actually turned on. In the technique of Japanese Patent No. 3872179, because the tail lamp is turned on only at night, the difference between the size of area of the tail lamp and the size of area of the brake lamp cannot be always obtained. On the other hand, in JP-A No. 9-267686, when the sunlight is strong, the lightness (luminance) attains the maximum level, and accordingly, the histogram distribution does not change at all. Like this, there is a problem in that the detection processing of the brake lamp may become unstable due to exterior environment.